Nodular cast iron and process of making same



United States Patent 2,841,488 NODULAR CAST IRON AND PROCESS OF MAKING SAME Henton Morrogh, Tanworth-in-Arden, England, assignor,

. by mesne assignments, to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware No Drawing. Application February 6, 1952 I Serial No. 270,281

7 Claims. (Cl. 75-123) This invention relates to the production of hypereutectic cast iron in which the graphite is present in the form of nodules.

.Three processes have been described in the patent and technical literature for the production of grey cast irons having graphite in the nodular form without the necessity of subsequent heat-treatment. In one of these processes the melt is alloyed with cerium, in another with magnesium, and in the third with calcium. In all of these processes the production of the graphite in the nodular form, as distinct from the normal flake form, is accompanied by improvements in mechanical properties of profound importance to industry. All three processes are technically similar but the production of nodular graphite by means of magnesium ofliers practical advantages. For instance, magnesium can give nodular graphite in both hypo-eutectic and hyper-eutectic irons, whereas cerium can only give nodular graphite inhypereutectic irons and those in which a deficiency of carbon is compensated for by 10% or more of nickel and/or copper. Cerium will dissolve easily in molten cast iron, and if magnesium is suitably alloyed with an excess of nickel, copper, iron or silicon, or some combination of these elements, in the presence or absence of others such as carbon, it will also dissolve easily. Calcium does not dissolve readily in cast iron. In all three cases the sulphur content of the treated iron must have a low value and in many cases the low sulphur content has to be obtained by using the desulphurising powers of the elements added. Magnesium is a more effective desulphurising agent than cerium and is more convenient to use for this purpose than calcium.

All this is well appreciated by those concerned with the art of producing nodular cast irons in the as-cast state and much research has been undertaken to perfect the art of producing nodular cast irons by means of magnesium. The conditions under which magnesium will give nodular graphite structures have been described in great detail. The iron treated must be capable of solidifying grey; after treatment the sulphur content of the iron should be below about 0.015% and the magnesium content of the iron must be above about 0.04% and preferably about 0.06%; after the magnesium has dissolved in the melt the liquid metal should be treated with a graphitising or inoculating addition such as ferro-silicon.

It has been pointed out that certain elements in the iron may have a deleterious eiiect on the magnesium process and in fact they may prevent the desired effects being obtained. In this connection it has been stated in British Patent No. 630,070 and in the corresponding U. S. Patent No. 2,485,760 that the presence of tin, lead, antimony, bismuth, arsenic, selenium and tellurium is detrimental, particularly inamounts approaching 0.1%. I have also found that titanium has similarly a deleterious effect. In addition copper has also been mentioned as a harmful element in amounts exceeding about 1% although, as has been indicated in the literature, coppermagnesium alloys can be used for the purpose of adding magnesium to cast iron. The exactmechanism by which ice these elements interfere with the desired function of magnesium is not known. Furthermore, those skilled in the art of producing nodular cast iron by means of magnesium have learned by experience that certain raw materials are satisfactory for the process whilst other raw materials of apparently the same or similar chemical analyses are, for no definitely known reasons, unsatisfactory. By raw materials we refer here to melting stock, that is, pig iron, steel and steel scrap, castliron scrap and refined pig iron which is, melted in the foundry to provide cast iron. By. unsatisfactory raw materials we mean those which when incorporated in the melt fail to give a cast iron in which all the graphite is nodular in spite of careful observance of the prescribed conditions as to carbon, silicon, manganese, phosphorus and sulphur content of the melt, addition of the magnesium, use of graphitising inoculants and correct casting. Some or all of the graphite carbon will then be in the undesirable form of flakes or lamellae in spite of correct treatment, in spite of correct analysis and in spite of a satisfactory magnesium content in the solidified casting. The presence of even a small amount of flake graphite in an iron having otherwise a nodular structure has a harmful effect on mechanical properties and the material may be non-ductile whereas the aim is to produce a shockresisting and ductile material.

The poor response of the raw materials found by the art to be unsatisfactory for treatment with magnesium has been very marked in those cast irons of hypereutectic compositionthat is, thoseirons having a carbon content of greater than 4.3--%(%Si+ P). Due to the fact that nodular cast irons show a marked tendency to unsoundness, on account of a high solidification shrinkage, unless elaborate precautions, wellknown to those skilled in the art, are taken, and since the tendency tov unsoundness is less the higher the carbon content, it is the high carbon or hyper-eutectic irons which the practical ironfounder would wish to use.

The consequence of these difliculties is that otherwise suitable raw materials such as pig iron, cast iron scrap,

process for the production of hypereutectic cast iron in.

which the graphite is present wholly or predominantly in nodular form. A further object is to produce such nodular hypereutectic cast iron by the .use of magnesium.

A still further object is to produce such nodular hyper;

eutectic cast iron from materials which fail to give a satisfactory nodular cast iron by the addition of magnesium by methods heretofore proposed. It is also an object of the invention to provide hypereutectic cast irons having markedly enhanced mechanical 7 properties due to the presence of both magnesium and cerium. A further:ob ject is to provide a process for the production of nodular hypereutectic cast irons with the help of copper-base alloys containing magnesium and cerium. Other objects will appear from the following description.

I have discovered a modification of the magnesium process whereby many otherwise unsuitable raw materials may be used to provide nodular cast irons of hypereutectic composition and also whereby greater consistency and reproducibility of properties is achieved. In addi-i tion, the modification to the process enables theproduc-j tion of a less bulky sulphide slagwhich is easier to handle inthe foundry and furthermore the use of the cheaper" Pbtented July 1,

copper-base alloys for adding magnesium is made possible'. i

The modification according to the invention comprises the addition of .a small amount of cerium either before, simultaneously with, or after the magnesium addition or together with the magnesiumin the form of an alloy, for instance, as a nickel-magnesium-cerium alloy or a copper-magnesium-cerium alloy. For the main purpose of this invention, which is to make it possible to produce nodular structures by addition of magnesium to unsuitable raw materials or irons containing copper, the cerium addition is equally effective when added prior to, simultaneously with or after the magnesium addition. In practice, however, it is found preferable to add the cerium in the form of an alloy of nickel, magnesium and cerium, or of copper, magnesium and cerium. When magnesium and cerium are added jointly in this manner the sulphide slag which appears on the surface of the metal, due to the desulphurising action of the addition, appears in less bulky form and is easier to remove from the surface of the metal. In addition the final sulphur content of the casting does not necessarily have to be reduced to the very low figure of about 0.015% which is necessary when magnesium alone is used, but may for instance be as high as 0.04% or even higher, and by the method of this invention nodular structures will still be obtained.

The mechanism by which the cerium offsets the unsuitability of the raw materials or the influence of copper is not known but it has been found to be effective and positive. The precise nature and amounts of the deleterious elements in many of the unsuitable raw materials is not known but irons containing up to 0.2% titanium and/ or up to 7% copper have been satisfactorily treated according to the invention with magnesium and cerium to give all or effectively all of the graphite in the form of nodules thus yielding materials of good mechanical properties.

The amount of cerium added may be small and by itself quite incapable of giving completely nodular structures or the high mechanical properties actually obtained. Generally a final cerium content of 0.01 to 0.02% will be satisfactory and is to be recommended although it may have any value from 0.001 to 0.2% or more depending on the raw materials. The efiects of the cerium and magnesium are not simply additive. For instance when the interfering element is copper in amounts over 2% it is possible to add as much as 0.1% or even 0.2% of magnesium without producing more than a very few graphite nodules in the microstructure, whereas 0.05% of magnesium together with 0.02% of cerium will give a good nodular structure with a very high level of mechanical properties in the castings so produced.

For the addition of cerium after or prior to the magnesium addition cerium mischmetall or an alloy of cerium or mischmetall with iron, nickel, copper or other elements may be used. For the addition of cerium in the form of an alloy with the magnesium, nickel-magnesium alloys and copper-magnesium alloys alloyed with cerium or mischmetall are quite suitable. Ferro-silicon-magnesium alloys are also suitable when alloyed with cerium or cerium mischmetall. Nickel base and iron base alloys may also contain carbon. Any combination of the elements nickel, iron, copper, silicon and carbon, together with magnesium and cerium or cerium mischmetall, can be used. Two examples of suitable alloys are indicated by the following compositions:

ALLOY NO. 1

Percent Magnesium 15 Cerium 4 Lanthanum and other rare earths 4 Carbon 1.5 Nicke1 75.5

ALLOY NO. 2

Percent Magnesium 15 Cerium 4 Lanthanum and other rare earths 4 Copper 77 The alloys may contain between 3% and 50% magnesium and between 0.5% and 20% cerium, but any convenient proportions of the two elements can be used.

When a hyper-eutectic nodular cast iron is required with consistency it is good practice according to the present invention to add magnesium and cerium, in the form of a suitable alloy with nickel or copper, to give 0.040.08% magnesium and 0.0l-0.03% cerium in the iron and then to inoculate the melt immediately before pouring with an addition of 0.20.6% of silicon in the form of ferro-silicon having 60-85% silicon.

In this description the term nodule has been used in the mineralogical sense of a small rounded lump. Graphite nodules can exist in cast iron in two forms-one which is usually spheroidal and has a radial structure referred to as spherulitic, and the other, which may be termed quasi-flake graphite, is less perfectly spheroidal or spherulitic and may be rounded lumps of graphite with no definite internal structure. From the point of view of the properties of the product this is of little importance since, provided the graphite is nodular, the mechanical properties of the casting are uniformly high Whether the nodules are spherulitic or not. The graphite structures produced may consist of a few perfect spherulites and the remainder of the graphite is a mixture of imperfectly formed spherulites and nodules which are not spherulitic, or they may be completely spherulitic depending on the inherent quality of the raw materials.

The process herein described as constituting this invention is applicable to hypereutectic cast irons and pig irons of a wide range of composition provided the iron will solidify grey. The silicon content can have any value up to 7%, the phosphorus any value up to 1.5%, the manganese any value up to 4%, chromium any value up to 4%, nickel any value up to 50%, molybdenum any value up to 2% and copper any value up to 8.0%. These elements can be tolerated singly or in any combination provided the iron will solidify grey.

The sulphur content of the iron to be treated can have any value up to 0.3% but for practical reasons well understood by those skilled in the art the sulphur content of the untreated metal should be as low aspossible.

After treatment with magnesium and cerium there should be not less than 0.005% magnesium and not less than 0.001% cerium in the solidified casting but the sum total of these two elements should not be less than 0.04% i and preferably the magnesium content should be within the range 0.04-0.08 and the cerium content within the range 0.01-0.03%. The final magnesium content can, however, have any value up to 0.25% and the final cerium content any value up to 0.2%.

A low sulphur content can be achieved before adding the magnesium and cerium by the use of any of the well known desulphurisation techniques such as the use of sodium carbonate or calcium carbide.

The metal to be treated can be melted in any of the conventional melting units such as a cupola, a rotary furnace, an electric arc furnace, a high frequency induction furnace or a crucible furnace.

The graphitising inoculant used can be added to the molten metal as a separate constitutent or the silicon required for inoculation can be combined with the magnesium and/ or the cerium in the form of an alloy, for

instance, as a nickel-silicon-magnesium-cerium alloy, an iron-silicon-magnesium cerium alloy or a copper-siliconrnagnesium-cerium alloy.

The metallic matrix of the iron can have any. structure produced either by the use of alloying elements and/or by heat-treatment-for instance, it may be pearlitic, ferritic, a mixture of pearlite and ferrite, marferro-silicon containing 80% silicon; Thechemical analyses and mechanical properties of the bars obtained are given below.

tensitic or austenitic. Any form of heat-treatment-an- Tapl Tap2 nealing, normalising, quenching, tempering and stressrelieving-can be app-lied to castings produced according Total Carbon, percent 3.78 3.80 to this inven ion for the purpose of obtaining special gggg g g ggt 123 ,128 mechanical properties. Sulphur, percent 0 012 0.030 The invention is illustrated but not limited by the gggigPggigfg 33 1 82 following examples. NickeLTpercentLI: 1105' 2100 Example I ante nae??? a 8:82 Ultimate Tensile Stress, Tons/sq. in 12. 2 44. 1 Two 50 lb. charges of a hypereutectic pig iron which Brine Hardness Number i 222 290 had previously been found to give unsatisfactory results with magnesium alone were melted separately in Sample 1 had all its graphite in the form of flake an oil-fired crucible furnace. The composition of the g p but SaIIIP1e 2 a all its graphite? in the pig iron before melting was: i form of nodules. It will be seen that the :final sulphur P t content of the metal treated with cerium and magnesium Total carbon 4,06 (sample No. 2) is appreciably higher than that of the Silicon 1.99 metal treated with magnesium alone (sample No. 1). Manganese 0.83 fSulphur 0.030 f 18 m Phosphorus 0.052 A hyper-eutectic pig 11011 of the following composit on Ni k l Less than" 002 was melted in an oil-fired crucible furnace. v Chromium 0.002 Percent Ti i 0.10 Total carbon u 4.00 Silicon -4 2.43 In both cases the molten metal was treated when the Manganese 0.78 temperature reached 1430" C. In the first melt the Sulphur 0.025 metal was treated with 6% oz. of a nickel-magnesium Phosphorus 0.050 alloy, 21 g. of cerium mischmetall and 2 /2 oz. of 80% Nickel 0.02 j ferro-silicon. In the second melt the molten metal was Chromium 0.002 treated only with 6% oz. of the same nickel-magnesium Copper Not detected alloy and 2 /2 oz. ferro-silicon. .The nickel-magnesium Molybdenum Not detected allow contained 12.2% magnesium. The analyses and Titanium 0.11 mechanical properties of clover-leaf test bars cast from Vanadium 0.01 each of these treated melts are given below. Aluminium 'Not detected T. 0., Si, Mn, 8, P, Ni, Mg, Ce, Ultimate Brinell No. Per- Per- Per- Per- Per- Per- Per- Per- Tensile Hardness cent cent cent cent cent cent cent cent; Stress, No.

Tons/sq. in.

Sample No. 1 had all its graphite in a nodular form This pig iron was found by experience to be unsatiswhereas Sample No. 2 had its graphite mainly in the factory for treatment with magnesium alone, mixtures of form of flakes With few 110(111165- flake graphite and nodular graphite being produced Example H instead of all the graphite being in the nodular form. 0 1b f th f n V Six portions each of lb. were taken and the metal 14 a zg gg g iggg compo Ion in the ladle in each case was treated as follows: was m e u an Percent 60 Tap 1.(No magnesium or cerium) 6 oz. 80% ferrosilicon. Qfffi. ffiff:11:33::::::::::::::::::::::::: iii? ceflum-mischmetalefi Manganese 0.71 5111mm 19 Tap 3.--120 g. cenum-m1schmeta1l-l-6 oz. 80% ferro- Phosphorus 0.049 sllicofl- Copper 2.00 Tap 4.8 oz. nickel-magnesium alloy+6 oz. 80%

ferro-silicon Two ta s each of 60 lb. were taken and after treatment of th e molten metal in the ladle two clover-leaf test Tap mckel'magnesmm 'i' 80% bars were cast from each tap. Tap No. 1 was treated with ferro'slhcon' 20 oz. of a nickel-magnesium alloy containing 12.2% P mckel'magneslllfn dmagnesium and 6 oz. ferro-silicon containing 80% f -l- Q farm-5111mm silicon. Tap No. 2. was treated with 24 oz. of a nickel- The nlckel-maglleslum alloy used contalfled 122%. magnesium-cerium alloy, containing 10.1% magnesium magnesium. and 3.33% cerium, 'and was then inoculated with 6 oz. A clover-leaf test bar was cast from each portion of metal The chemical analyses and mechanical properties of the resulting bars are given below.

, 8 a about 0.2% and copper in amount of from about 2% to 7%, which process comprises establishing a meltof T. 0., Si, Mn, S, P, Ni, Mg, Ca, Tensile Brinell N0. Treatment perperperperperperperper- Strength, Hardness cent cent cent cent cent cent cent cent Tons/sq. N o.

Inoculation nly 3. 71 2. 84 0. 70 0. 031 8. 8 176 Misehmetall 3. 75 2. 86 0. 67 0. 018 25. 6 210 (lo 3. 08 2. 84 0. 7t) 0. 015 25. 7 215 Ni-Mg Alloy r. 3. 77 2. 88 O. 68 0. 010 31. 6 262 Ni-Mg Alloy then Mischmetall 3. 73 2. 94 0. 69 0. 000 40. 6 243 Example IV 270 lb. of a cast iron of the following composition was melted in an oil-fired crucible furnace.

I Percent Total carbon 4.07

Silicon 1.79 Manganese 0.51 Sulphur 0.120 Phosphorus 0.047

Four taps each of 60 lb. were taken and treated as follows:

Tap 1.--7 oz.nickel-magnesium-cerium alloy+6 oz. 80% ferro-silicon.

Tap 2.16 oz. nickel-magnesium-cerium alloy+6 oz. 80% ferro-silicon.

Tap 3.20 oz. nickel-magnesium-cerium alloy+6 oz. 80% ferro-silicon. v

Tap 4.-24 oz. nickel-magnesium-cerium alloy+6 oz. 80% ferro-silicon.

The nickel-magnesium-cerium alloy contained 10.1% magnesium and 3.3% cerium.

Clover-leaf test bars were cast from each ladle of metal. The chemical analyses and mechanicalpropertie grey cast iron hypereutectie in relation to carbon content and containing an interfering amount of at least one of said group of interfering elements, adding magnesium and cerium to said molten hypereutectic iron in such amounts that the iron, when cast, contains not less than 0.005% of magnesium and not less than 0.001% of cerium, the total of these two metals being at least about 0.04%, said cast iron being characterized by a satisfactory nodular graphite structure despite the presence of said detrimental amounts of elements capable of interwhich interferes with the substantially complete graphitenodularization of the free carbon by magnesium alone in the iron when cast.

4. A process for producing magnesium-containing hypereutectic cast iron as defined in claim 1, in which said melt contains an element selected from the group consisting of tin, lead, antimony, bismuth, arsenic, selenium and tellurium in detrimental amount up to about 0.1%.

'5. A process as defined in claim 1, wherein the magnesium and cerium when added to the molten bath are alloyed with a metal selected from the group consisting of nickel, copper and iron, and a silicon-containing inoculant is thereafter added to the bath.

obtained are given below. 6. A process as defined in claim 1, wherein the mag- I T. (1., Si, Mn, S, P, Ni, Mg, Ce, Tensile Brinell N0. perperperperperperperper- Strength, Hardness cent cent cent cent cent cent cent cent Tons/sq. N0.

Sample No. 1 had all its graphite in the flake form but samples Nos. 2, 3 and 4 had all the graphite in the nodular form. The sulphur contents of samples 2, 3, and 4 are all much'higher than could be tolerated for the production of nodular structures by magnesium alone.

I claim: 7

1. A process for producing magnesium-containing hypereutectic nodular cast iron from molten cast iron containing an interfering element detrimental to the graphitenodularizing action of magnesium alone, said element being in the group consisting of tin, lead, antimony, bismuth, arsenic, selenium and tellurium, in detrimental nodular graphite, which cast iron contains amounts of an element interfering with the nodularizing action of magnesium alone, said interfering element being in the group consisting of tin, lead, antimony, bismuth, arsenic, selenium and tellurium in detrimental amount up to about 0.1%, copper in detrimental amount from about 2% amount "up'to about 0.1%, titanium in amount up to to about 7% and titanium in detrimental amount up to 9 about 0.2%, said iron as cast also containing not less 2,603,563 than 0.005% magnesium and not less than 0.001% 2,622,022 cerium, the total of the last two said elements being at least 0.04%.

References Cited in the file of this patent UNITED STATES PATENTS 2,542,655 Gagnebin Feb. 20, 1951 10 Crome July 15, 1952 Crome Dec. 16,. 1952 FOREIGN PATENTS France Apr. 15, 1953 

1. A PROCESS FOR PRODUCING MAGNESIUM-CONTAINING HYPEREUTECTIC NODULAR CAST IRON FROM MOLTEN CAST IRON CONTAINING AN INTERFERING ELEMENT DETRIMENTAL TO THE GRAPHITENODULARIZING ACTION OF MAGNESIUM ALONE, SAID ELEMENT BEING IN THE GROUP CONSISTING OF TIN, LEAD, ANTIMONY, BISMUTH, ARSENIC, SELENIUM AND TELLURIUM, IN DETRIMENTAL AMOUNT UP TO ABOUT 0.1%, TITANIUM IN AMOUNT UP TO ABOUT 0.2% AND COPPER IN AMOUNT OF FROM ABOUT 2% T 7%, WHICH PROCESS COMPRISES ESTABLISHING A MELT OF GREY CAST IRON HYPEREUTETIC IN RELATION TO CARBON CONTENT AND CONTAINING AN INTEFERING AMOUNT OF AT LEAST ONE OF SAID GROUP OF INTERFERING ELEMENTS, ADDING MAGNESIUM AND CERIUM TO SAID MOLTEN HYPEREUTECTIC IRON IN SUCH AMOUNTS THAT THE IRON, WHEN CAST, CONTAINS NOT LESS THAN 0.005% OF MAGNESIUM AND NOT LESS THAN 0.001% OF CERIUM, THE TOTAL OF THESE TWO METALS BEING AT LEAST ABOUT 0.04%, SAID CAST IRON BEING CHARACTERIZED BY A SATISFACTORY NODULAR GRAPHITE STRUCTURE DESPITE THE PRESENCE OF SAID DETRIMENTAL AMOUNTS OF ELEMENTS CAPABLE OF INTERFERING WITH THE GRAPHITE-NODULARIZING ACTION OF MAGNESIUM. 